Photographic direct positive matrix process



Patented Aug. 28, 1951 rno'rooaarmo DIRECT POSITIVE; MATRIX PnooEss- Anthony MarriageyHa rrow, England, assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application May 13, 1949, Serial Ni). 93,197. In Great Britain May-27; 1948 This invention relates to the production of photographic relief images, especially dye-transfer'matrices for use in colour photography.

When making colour prints from positive colour transparencies by the dye-transfer process it is very desirable to be able to produce positive gelatine dye-matrices directly from such transparen'c'ies by a "reversal "process using silver halide emulsions and without intermediate negatives.

The most successful attempts at doing this in the past have used a hardened emulsion containing a grey dye or pigment. This was exposed from the topsurface, develbped and treated with an etch-bleach bath. Thepurposeof the dye or pigment was to restrict the penetration of the exposure light so that-instead of causing silver tobedevelopable more or lesshhiformlythroughout the depth of the layer the exposure renders developablemost of the halide within a compact layer, the thickness of which varies with the exposure. While this achieves its purpose of giving good gradation and sharp differentiation between hard and soft gelatine (and hence reliability and reproducibility ofthe relief-making) it accentuates the need for a very uniform coating thickness of emulsion. For if a slightly uneven coating i'sgive'n 'a uniform exposure suilicientto render soluble (after processing) nearly but not quite the w-hole layer, the relief left after removing a uniformthickness of emulsion from a slightly uneven thickness will be relatively very uneven. It is therefore very 'diflicult with such a material to makepic'tures that do not have uneven'highlights.

'Qn'e method of overcoming this difficulty which has been proposed consists in exposing a layer of unhardehed' photographic emulsion under a negative; developing the layer in a, non-tanningdeveloper and-after, removing the developed sil ver, dyeing the" layer to increase its absorption ofactiniclight; The dyed layer is then exposed through the support to'a suitable light and developedwith tanningdeveloper. After bleachmg and removal ofthe unharde'ned gelatin there.

9 Claims. (01. es-5.6

emulsion may be defined as one which, when a test portion is exposed to a light intensityscale for a fixed time between and 1 second, and developed for 4 minutes at 20 C. in the ordinary; surface developer (Example I) exhibits a maximum density not greater than /5 the maximum density obtained when the same emulsion equally exposed and developed for 3 minutes at 20 C. in an "internal type developer (Example II); Preferably the maximum density obtained with the"surfacedeveloper is not greater than the maximum density'obtained when the same emulsion is develop-ed in the internal type developer. Stated conversely; an internal latent image emulsion, when developed in an interna type developer (Example 11) exhibits a maximum density at least-5, and preferably at least 10, times the maximum density-obtained when the same emulsioni's exposed in the same way and developed in a surface"- developer (Example I). It is an object-of my invention to provide a method of producing photographic relief images by a reversal process which is considerably simpler than the processesproposed hitherto. Another object is to providea method of producing reversalreliei images-which is independent of variations in the'thickness of coating of the emulsion layer. -Another object-is to provide a; process in which the emulsion layer retains a high effective speed to thesecond' exposure. Yet another objectis to provide a process in which dyeing of the emulsion layer after the first exposure is un-' necessary. s

In the case where the emulsion layer does not possess-a sufiiciently high absorption of the radiation used for the second exposure the layer may be treated in any desired manner to cause it to restrict 'thepenetration of such radiation throug-h the layer.

The first exposure, which is made to any desired image, may be made directly on theemulsion layer but for mostpurposes, such as in the production of dye-transfermatrices, it will be preferable-to perform this exposure through the support. The degree of exposure should be such as to cause progressive desensitisation of the layer over the-range'of exposures in the image. It isa characteristic property of internal image emulsions as used in this invention that the latent image produced by the first exposure is formed mostly inside the silver halide grains and very little ornosurface latent image isformed. By treating suchan emulsion carrying an internal latent image with a suitable reversing solution.

the "silver halide grains can be made capable of forming a surface image on a second exposure but the sensitivity to such second exposure will be decreased by the first formed latent image. The reversing solution may be an ordinary developing solution or a developer of low activity, the developing agent being an organic developer having little or no solvent action on silver halides, and in the case of some emulsions the reversing treatment may consist in soaking the emulsion in plain water only. For further details regarding emulsions of this type see, for example, U. S. Patent 2,456,953, Knott and Stevens, and U. S. application Serial No. 82,914, Davey and Knott, filed March 22, 1949.

The sequence of operations after the first exposure and the reversing treatment will then depend on the properties of the sensitive emulsion layer used in the process. Thus, if the layer is such that it strongly absorbs the radiation to be used for the second exposure but does not strongly absorb the image-forming light of the first expo sure, the layer may be subjected to the second exposure without further treatment. Thus, in the preferred form of the invention there is used for the sensitive layer an emulsion of the internal-image type having a relatively high silver iodide content, preferably not less than 6% calculated on the total silver halide. Such emulsions havebeen described in U. S. application Serial No. 82,914, Davey and Knott, filed March 22, 1949, and are characterized by an unusually high absorption of near ultra-violet light. Therefore, the second exposure is made by exposing the layer uniformly, after the first exposure and treatment with reversal bath, to ultra-violet light through the support. Owing to the high absorption of the iodine-containing emulsion the penetration of the ultra-violet light through the layer will be restricted to only a portion of its depth and the developable image will be correspondingly restricted. One very great advantage of the use of internal-image emulsionslies in the fact that, even after the first exposure, the emulsion retains a high sensitivity for the second exposure and an ample amount of ultra-violet light for this purpose can therefore be obtained from a tungsten filament lamp and ultra-violet filter, thus avoiding the necessity for using mercury vapour lamps or other expensive source of ultra' violet light. The second exposure can be given side after the emulsion has been immersed in the reversing bath for the desired time but before removing it therefrom. This procedure has the advantage that it is notnecessary to wipe off" the surplus bath from the support on removing the sensitive element from the reversing bath which is otherwise necessary if a uniform second exposure is to be obtained. The reversing bath can if desired, be combined with or constituted by the developer for the surface latent image, e. g., a tanning developer, but in this case the second exposure must be completed before appreciable development of the image occurs. The reversing solution may be the developer for the surface latent image Without the alkaline constituents.

In an alternative procedure according to the invention which may be adopted when the sensitive emulsion does not absorb ultra-violet light sufiiciently there may be incorporated in the layer, either during its preparation or by bathing '4 after coating, a dye or pigment, preferably nonfiuorescent, which absorbs ultra-violet light. Such a dye must not have an absorption in a part of the spectrum which would cause serious interference with the light used for the imagewise exposure.

In yet another alternative procedure the emulsion layer may be treated after the first exposure to render it absorbent of radiation which can be used for thesecond exposure, for example, by dyeing the layer with a dye, such as a yellow dye, and using light of a complementary colour, e. g., blue light, for the second exposure, which is made through the support.

The dye used should of course not desensitize the emulsion layer unduly; the emulsion must retain sufficient sensitivity to be given the second exposure in a convenient time and manner. It is particularly advantageous to use a dye or mixture of dyes which have a broad absorption band and thus will absorb at all wavelengths to which the emulsion layer is sensitive. If the absorption of the dyes is relatively high throughout the spectrum the second exposure can be made with unfiltered light after the layer is dyed. The dye or dye mixture should preferably be approximately neutral but may be, for instance, brown. It must be able to diffuse through the emulsion layer in a reasonable time. ing a broad absorption band has the advantage that any slight fogging of the emulsion which might occur when the surplus dye solution is being removed from the sensitive material after treatment with the dye solution does not harm the final relief image.

Examples of dyes which may be used in accordance with this form of the invention, either alone or in admixture are: Xylene Red B (Color Index No. 748), Naphthol Green B (Color Index No. 5) and Acid Brown J (Color Index No. 239); Xylene Red, when used alone requires a green light for the second exposure of the emulsion layer. A dye solution which has been found to be very suitable for this purpose is one having the following composition:

Naphthol Green B "gm" 30 Emulsion layers dyed with this solution may be re-exposed to unfiltered light. A solution of Acid Brown containing 30 gm. per litre has also been found to be very suitable and the layers dyed therewith may likewise be re-exposed to white light. It is often advantageous to incorporate the dye or dyes in the reversal bath, but care should be taken to remove surplus solution from the element before the second exposure.

However, in order to avoid the necessity for wiping off surplus dye from the sensitive material a pigment may be formed in situ by incorporating in the sensitive emulsion layer a substantially colorless component and bathing the layer after the first exposure in a solution of another colorless component. Such components must be innocuous, i. e., they must not destroy any internal latent image formed by the first exposure nor destroy the sensitivity to the second exposure, nor harden the gelatine or other colloid binder of the emulsion. For example, a colorless color coupler may be incorporated in the emulsion which is treated after the first exposure with an alkaline diazonium solution to The use of dyes hav-' produce a colored pigment within the emulsion layer.

Another method of performing the invention consists in using for the sensitive layer an internal-image emulsion to which there has been added a proportion of a completely fogged emulsion of the usual silverhalide type, especially a gelatino-silver chloride emulsion. The added emulsion may be fogged by light or chemical action and the proportion added may be of the order of 5% in molar proportions or even up to 15%. Still greater proportions may be required in the case of emulsions giving a silver deposit of lower covering power than silver chloride. By choosing a reversal bath of suitable composition the fogged emulsion grains may be developed on immersing the layer in the bath without affecting the ability of the remaining emulsion to form a surface latent image during the second exposure.

In the simplest form of the present invention the "second exposure is made by exposing the emulsion layer to active radiation which is uniformover the whole area of the layer. In a valuable modification of the invention which is particularly useful for the production of corrected color separation images, the second exposure is not uniform but consists of an imagewise exposure controlled by a different color separation image from that controlling the first exposure, as hereinafter described.

3 When the sensitive material has been treated according to any of the foregoing methods and given the second exposure it is developed, preferably with a tanning developer, i. e., a developer which hardens the layer Where silver is devel oped, but a developer of the more usual nontanning type followed by a tanning bleach solution may be used, except in the case where a fogged silver halide emulsion is incorporated in the layer. If the reversing solution retained by the layer would intefere with the tanning developer, the layer should be washed before development. It is, therefore, desirable to choose a reversing bath which does not so interfere. When the tanning process is completed the layer is washed in hot water to remove the unhardened gelatin in the usual manner.

If the reliefs made by the methods described above take the form of color separation images made from a colored positive original by the use of color-sensitized emulsions and by making the first exposure with suitably colored light, the reliefs obtained will be positive images which can be dyed and used as dye-matrices for the preparation of colored prints by the dye-transfer process.

An important application of the method of the present invention consists in the production of reversed color separation relief images incorporating color correction similar to that given by the well-known masking method. For this purpose the second exposure is not uniform but consists of an image-wise exposure controlled by a different separation image from that controlling the first exposure.

Clearly, if the final relief is still to be a reversed image, the density of the relief must vary more rapidly with the logarithm of the first exposure than with that of the second exposure. it the separations are of similar contrast. In other words, either the "desensitization-contrast must be greater than unity or the contrast of the separations used for the second exposur must be less than that of the first.

6' For example, suppose that it is desired tomake from a color transparency a magenta-printing matrix in which some correction for the unwanted green absorption of thecyan dye is introduced. The matrix material is given a first exposure (either by' contact or projection) behind thetransparency, using a green filter. It is then processed if necessary, as hereinbefore described according to the type of sensitive material in use, replaced in the exposing apparatus and given a second exposure having an intensity controlled by the cyan dye of the transparency. This exposure may be made with the same red :filter as will be used for making the cyan matrix provided that the desensitization-contrast is greater than unity; if not, it may be made with an infrared or other filter passing light that is not so strongly absorbed by the cyan dye as that passed by the red filter (but which is not absorbed, or little absorbed, by the other dyes). v

The amount of correction obtained can be controlled partly by the exposing conditions and partly by the emulsion and its processing. The printing operations are simplified if the same set of filters is used for all separations, the correction being adjusted by having suitable desensituation-contrast.

Registration of the two exposures is also made simpler if the image is made slightly unsharp for the second exposure. If the exposures are made by projection it is possible to achieve this and at the same time correct for expansion of the film-base between exposuresby placing the film for the second exposure at a slightly greater distance from the lens.

An ordinary, surface type developer, that is, one which develops an image only on the surface of the grains of an internal latent image emulsion, is the following:

"EXAMPLE I p-Hydroxyphenylglycine g .10 Sodium carbonate (crystals) g Water to liter 1 Development time, 4 min. at 20 C. 7

An "internal type developer, that is, one which develops an image inside the grains of an internal latent image emulsion, is the following:

Development time, 3 min. at 20 C.

The invention is further illustrated by the following examples of the method of making color separation relief images Without masking:

EXAMPLE III An unhardened internal image type of emulsion having "a relatively high silver iodide content was prepared according to Example II, of United States application Serial No. 82,914, Davey and Knott, filed March 22, 1949. The emulsion was dye sensitized to render it panchromatic and coated on-a transparent support. The resulting element was exposed to red light through the support in contact with a positive color trans? parency. The exposed element was then soaked for 1 /2 minutes in the following bath:

Pyrogallol gm 5 N-methyl-p-aminophenol sulfate gm 1 Sodium metabisulphite gm 1 Water to cc 1000 No visible image developed at this stage. The soaking of the element was performed in a dish with a glass base and the element was exposed through the base of the dish and through the support to ultra-violet light from a tungsten filament lamp fitted with a filter which cuts off all visible light but transmits ultra-violet.

The solution in the dish was then poured off and mixed with an equal volume of the following solutionr Potassium carbonate gm 200 Potassium bromide gm 1 Water to", liter 1 The mixed solution was poured back into the dish and development continued for 7 minutes. The

.element was then washed in hot water until all soluble gelatin had been removed and the relief obtained on drying was used for the production of colored prints by dye transfer in the usual man- In this example it is not essential to use the two developer solutions separately as described above; if desired, the element may be soaked in the mixed developer after the first exposure, but in this case it is essential to complete the second exposure (1. e. the exposure to ultra-violet light) before any apreciable development has occurred and it will generally be found to be more convenient to use the solutions separately.

EXAMPLE IV,

A glass plate was coated with a layer of the unhardened internal-image type emulsion described in Example II of United States application Serial No. 82,914, Davey and Knott, filed March 22, 1949, the emulsion being dye-sensitized to green light.

The emulsion was exposed in contact with a positive color transparency using green or blue light. The Plate was then soaked for two minutes in the following developer:

Catechol gm 5 Sodium sulphite (anhydrous) gm 1 Sodium carbonate (anhydrous) gm 8 Tartrazine N. S gm 40 Water to ml 1000 The plate was removed from the developer and all surplus dye wiped off the back. The plate was then exposed through the back to violet light using a Wratten safelight with a Wratten No. 35 violet'filter and a Photofiood lamp. Development was carried out with the following tanning developer:

Solution A Pyrogallol gm 5 N-methyl-p-aminophenol sulfate gm 1 Sodium metabisulphite gm 1 Water to cc 1000 Solution B Potassium carbonate gm 200 Potassium bromide gm 1 Water to cc 1000 For use take equal volumes of Solutions A and B.

After development the plate was rinsed for 1' minute in a stop bath of 1 acetic acid, washed in hot water to remove the soluble colloid and dried. The relief so obtained was used for dye transfer in the production of colored prints in the usual manner.

EXAMPLE V The internal-image type of emulsion used for Example IV was mixed with 5% by moles of a gelatino silver chloride emulsion which had been fogged by stirring in daylight until quite deeply colored and the resulting emulsion was coated on glass plates. After exposure behind a nega- This solution developed the grains of fogged emulsion but caused no appreciable development of the exposed internal-image emulsion. The plate was then exposed through the back for 30 seconds at 30 inches from a 25 watt lamp and washed for 2 minutes in running water. The plate was developed in the tanning developer given in Example IV above and washed in hot water to form the relief.

I claim:

1. A method of producing a photographic relief image comprising the steps of exposing to an image-forming light a photographic element comprising a layer of an unhardened sensitive silver salt emulsion a test portion of which upon exposure to a light intensity scale for a fixed time between and 1 second and development for 3 minutes at 20 C; in the following internal type developer (II) Hydroquinone grams 15 Monomethyl para-aminophenol sulfate do 15 Anhydrous sodium sulfate do 50 Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulfate do 20 Water to liter 1 gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Para-hydroxyphenyl glycine grams 10 Sodium carbonate do Water to liter 1 treating the emulsion to render it capable of forming latent image developable by the aforesaid developer (I), without appreciably developing the first-formed latent image to a visible image, subsequently uniformly exposing the emulsion layer through the support to radiation to which the emulsion is sensitive and the penetration of which through the emulsion is restricted to a greater extent than said imageforming light, developing the surface latent image formed by the said radiation, tanning the layer where silver is thereby produced and removing the untanned colloid of the layer.

2. A method of producing a photographic relief image comprising the steps of exposing to an image-forming light a photographic element comprising a layer of an unhardened sensitive silver salt emulsion containing not less than 6 by mols Hydroquinone grains 15 Monomethyl para nephenel su1fate do 15 Anhydrous sodium suuat'en d'o 50 Potassium bromide do 10 Sodium hydroxi e 'do 25 Sodium thioslllfate do 20 Water to liter 1 gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion developed for 4 minutes at 20 C. in the following surface developer (I) Para-hydroxyphenyl glycine "grams" Sodium carbonate do 100 Water to -1 liter 1 treating the emulsion to render it capable of forming late'n't image developable by the aforesaid developer (I), without appreciably developing the first-formed latent image to a visible image, subsequently exposing the emulsion layer through the support to uniform ultra-violet light, developing the surface latent image formed by said ultra-violet light, tanning the layer where silver is thereby produced and removing the untanned colloid of the layer.

3. A method of producing a photographic relief image comprising, the steps of exposing to an image-forming light aphotographic element comprising a layer of an unha'rdened sensitive silver salt emulsion containing not less than 6% by moles of silver iodide calculated on the total silver halide content, atest portion of which upon exposure to a light intensity scale for a fixed time between and 1 second and development for 3 minutes at C. in the following internal type developer (II gives a maximum density at least 5 times the maximum density obtained' when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Para-hydroxyphenyl glycine grams 10 Sodium carbonate do 100 Water to liter 1 then. without developing the latent image so formed to a visible image, soaking the exposed layer in a solution containing a photographic developing agent whereby the emulsion is made capable of forming latent image developable by the aforesaid developer (I), but said latent image is not appreciably developed, subsequently exposing the emulsion layer through the support to uniform ultra-violet light, developing the surface latent image formed by said ultra-violet light with a tanning developer and removing the untanned colloid of the layer.

4. A method of producing a photographic relief imagecomprisihg the steps of ex osing-to an image forming light aphotographic-element com-' prising a layer of an unhardened sensitive silver salt emulsion, a test portion of which upon exposure to a light intensity scale for a fixed time between -an'd 1 second and development for 3 minutes at 20 C. in the following internal type developer (II):

Hydroquinone grams 15 Monomethyl para-'aminophenol sulfate I do l5 Anhydrous sodium sulfate do 50 Potassium bromide 1; 1do 1 10 Sodium hydroxide 1 do 25 Sodium thiosulfate do 20 \Water, to liter 1 gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emuls ion is developed for 4 minutes at 20 C. in the following surface developer (I):

Para-hydroxyphenyl glycine gramm 10 Sodium carbonate do 100 Water to- -1;-411;e liter 1 treating the emulsion to render capable of forming latent image developable by the aforesaid developer (1), without appreciably developing the latent image formed by the said exposure, incorporating a light absorbing substance in the layer, exposing the layer uniformly through the support to light of a color absorbed by the said light-absorbing substance and to which the emulsion is sensitive, developing the latent image so formed with a tanning developer and removing the untanned colloid of the layer.

5. A method of producig a, photographic relief image comprising the steps of, exposing to an image-forming light a photographic element comprising a, layer of an unhardened sensitive silver salt emulsion, a test portion of which upon exposure to a lightintensity scale for a fixed time between and 1 second and development for 3 minutes at 20 C. in the following internal type developer (II): I

Monomethyl para-aminophenol sulfate do' 1'5 Anhydrous sodium sulfate- .;do '50 Potassium bromide do 10 Sodium hydroxide fl do 25 Sodium thiosulfate do' 20 Water to liter 1 gives a maximum density at least 5 times the maximum density obtained when the equally ex posed silver halide emulsion is'3 developed for 4 minutes at 20 C; inthe following surface developer (I):

Para-hydroxyphenylglycine grams 10 Sodium carbonate do 100 Water to 1 liter I 1 11 image comprising the steps of exposing through the emulsion layer to an image-forming light a photographic element comprising a layer of an unhardened sensitive silver salt emulsion, a test portion of which upon exposure to a light intensity scale for a fixed time between yioo and 1 second and development for 3 minutes at 20 C. in the following internal type developer (II) Hydroquinone l grams 15 gives a maximum density at least times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Para-hydroxyphenyl glycine grams Sodium carbonate do 100 Water to iter" 1 said image-forming light being capable of penetrating through at least a substantial proportion of the depth of said emulsion layer, treating the emulsion to render it capable of forming latent image developable by the aforesaid developer (1), without appreciably developing the latent image formed by the said exposure, treating the emulsion layer with a solution of a, dye, exposing the layer uniformly through the support to light of a color absorbed by the dye and to which the emulsion is sensitive, developing the latent image so formed with a tanning developer and removing the untanned colloid of the layer.

7. A method of producing a photographic relief image comprising the steps of exposing to an image-forming light a photographic element comprising a layer of an unhardened sensitive silver salt emulsion, a test portion of which upon exposure to a light intensity scale for a fixed time between i and 1 second and development for 3 minutes at C. in the following internal type developer (II) gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Para-hydroxyphenyl glycine grams 10 Sodium carbonate do 100 Water to liter 1 treating the emulsion to render it capable of forming latent image developable by the aforesaid developer (I), without appreciably developing the latent image formed by the said exposure, treating the emulsion layer with a solution of a yellow dye, exposing the layer uniformly through the support to blue light, de-

veloping the latent image so formed with a tanning developer and removing the untanned colloid of the layer.

8. A method of producing a photographic relief image comprising the steps of exposing to an image-forming light a photographic element comprising a layer containing a mixture of an unhardened sensitive silver salt emulsion, a test portion of which upon exposure to a light intensity scale for a fixed time between and 1 second and development for 3 minutes at 20 C. in the following internal type developer (II) Hydroquinone -grams 15 Monomethyl para-aminophenol sulfate do 15 Anhydrous sodium sulfate do 50 Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulfate do 20 Water to liter 1 gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Para-hydroxyphenyl glycine grams 10 Sodium carbonate do 100 Water to liter 1 and a fogged silver salt emulsion, developing the said fogged emulsion and, without appreciably developing the latent image in the first mentioned emulsion, rendering such emulsion capable of forming latent image developable by the aforesaid developer (I), subsequently uniformly exposing the emulsion layer through the support to radiation to which the unfogged emulsion is sensitive, developing the latent image formed thereby, in a tanning developer and removing the untanned colloid of the layer.

9. A method of producing a photographic relief image comprising the steps of exposing to an image-forming light a photographic element comprising a layer containing a mixture of an unhardened sensitive gelatino-silver halide emulsion, a test portion of which upon exposure to a light intensity scale for a fixed time between A and 1 second and development for 3 minutes at gives a maximum density at least 5 times the maximum density obtainedwhen the equally exposed silver halide emulsion'is developed for 4 minutes at 20 C. in the following surface developer (I):

Para-hydroxyphenyl glycine grams 10 Sodium carbonate do 100 Water to ter 1 and a fogged gelatino-silver chloride, emulsion, treating the layer with a non-tanning photographic developer which develops the fogged silver chloride emulsion but doesnot appreciably 13 develop the internal latent image of the firstmentioned emulsion and renders such emulsion capable of forming latent image developable by the aforesaid developer (I), subsequently exposing the layer uniformly through the support to 5 light to which the unfogged emulsion is sensitive, developing the latent image formed thereby in a tanning developer and removing the unhardened colloid of the layer.

ANTHONY MARRIAGE.

14 REFERENCES CITED UNITED STATES PATENTS Name Date Capstafi Feb. 10, 1925 OTHER REFERENCES American Photography, December 20, 1926, pages 664 and 666.

Number 

1. A METHOF OF PRODUCING A PHOTOGRAPHIC RELIEF IMAGE COMPRISING THE STEPS OF EXPOSING TO AN IMAGE-FORMING LIGHT A PHOTOGRAPHIC ELEMENT COMPRISING A LAYER OF AN UNHARDENED SENSITIVE SILVER SALT EMULSION A TEST PORTION OF WHICH UPON EXPOSURE TO A LIGHT INTENSITY SCALE FOR A FIXED TIME BETWEEN 1/100 AND 1 SECOND AND DEVELOPED FOR 3 MINUTES AT 20* C. IN THE FOLLOWING INTERNAL TYPE DEVELOPER (11): 